Bring your stethoscope, a pen or two, and the proper uniform. That really should be all you need! You are on orientation to learn how to do the job! (that by the way they already hired you for... so GOOD JOB!) You already have a LVN degree so you obviously have some knowledge; just stay calm and remember what you have learned in school. Most orientations start with touring the facility, meeting staff, and sometimes watching videos. However, you may start on the floor orientation right away and for that you should be mentally prepared to do what you have been hired for; keep in mind that you have an orientator that is there to help you - use them, watch them, and ask questions!
Each facility has it's own policy and procedures. You will never be expected to know a facilities policy and procedures before you go to your orientation. Also keep in mind that schooling is a basis... you aren't expected to know everything!